Stem cells are cells having both the property of pluripotency, whereby cells differentiated into different cells are produced, and self-replication, whereby identical cells are produced by cell division. Stem cells derived from the embryo at the early stages of development of the fertilized ovum are known as embryonic stem cells (ES cells). Human ES cells hold promise for use in regenerative medicine, but ethical problems involved in the use of fertilized eggs has prevented the creation of new human ES cells.
Recently, induced pluripotent stem cells (iPS cells) have also been the focus of attention, as cells having properties similar to ES cells. However, numerous problems including cell canceration and creation efficiency have been encountered in the creation of iPS cells. On the other hand, somatic stem cells, which have the ability to differentiate into specific tissues, are obtained from the patient's own body tissues such as bone marrow, for example, and therefore do not involve the ethical problems associated with embryonic stem cells.
Epidermal stem cells (Non-patent document 1) are well known to be present in the basal epidermal layer of skin, and follicular epithelial stem cells (Non-patent document 2) or melanocyte stem cells (Non-patent document 3) have been reported in a region known as the follicular bulge region. On the other hand, fibroblasts having elongated spindle shapes are present in fiber components in the dermis that are composed mainly of collagen, but it has not yet been determined whether or not stem cells are present in dermal fibroblasts. Also, while it is known that skin-derived precursors (SKP) that differentiate into multiple cell lines such as fat, glia, cartilage and muscle are present in the skin (Non-patent document 4), the relationship between dermal fibroblasts and SKP has not been elucidated.
Mesenchymal stem cells that have separated from the bone marrow as fibroblast precursors (Non-patent document 5) differentiate into a variety of cells of the mesenchyme (bone cells, muscle cells, chondrocytes, tendon cells, adipocytes and the like), and therefore their application in regenerative medicine for reconstruction of bone, blood vessels and muscle is promising. Recently it has been suggested that they may be abundantly present in tissue that contains mesenchymal tissue, and mesenchymal stem cells have been isolated from fat, umbilical cord and placenta as well (Non-patent documents 6-8).
Recent findings have shown that mesenchymal stem cells are present in systemic blood vessels as pericytes and function to maintain vascular stabilization and tissue homeostasis (Non-patent documents 9 and 10).
When blood vessels are destroyed at sites of tissue damage or its periphery, the mesenchymal stem cells, or pericytes, separate from the blood vessels and proliferate to supply the lost cells (Non-patent documents 11-14) while releasing bioactive factors to protect tissue (Non-patent documents 15-19) and functioning to repair and regenerate the damaged tissue. It has been reported that these secreted factors function not only for angiogenesis and anti-apoptosis, but also to powerfully inhibit immunity (Non-patent documents 21 and 22), and to suppress destruction of tissue damaged by T cells or B cells (Non-patent documents 9 and 22).
In addition, mesenchymal stem cells are known to exhibit antifibrinolytic action (Non-patent documents 23 and 24) and effects against multiple sclerosis and diabetes (Non-patent document 9).
On the other hand, it is becoming clear that chronic inflammation is a fundamental pathology common to a variety of conditions (for example, metabolic syndrome, arteriosclerotic disease, cancer, neurodegenerative disease and autoimmune disease) (Non-patent document 25). For example, it has been reported that endothelial cell dysfunction and insulin resistance are induced by chronic inflammation, leading to various diseases such as diabetes or arteriosclerotic disease (Non-patent document 26). Furthermore, it has been found that obese adipose tissue itself leads to inflammatory changes (Non-patent documents 27-29). The fact that chronic inflammation occurs in the vicinity of blood vessels suggests that chronic inflammation also involves a failure of interaction between mesenchymal stem cells, which are pericytes, and blood vessels.
Based on this knowledge, it is believed that promoting the production of, and stabilizing, mesenchymal stem cells, would be highly effective for a variety of purposes, including vascular stabilization, maintaining tissue homeostasis, repair and regeneration of damaged tissue, preventing fibrosis, preventing and treating diseases such as multiple sclerosis and diabetes and preventing and ameliorating conditions associated with chronic inflammation, such as metabolic syndrome.
The present inventors have already reported that mesenchymal stem cells are present in the dermis as well, and have established a method for efficiently isolating mesenchymal stem cells from the dermis (Japanese Patent Application No. 2009-213291). Considering the function of mesenchymal stem cells described above, it is believed that stabilizing and promoting the production of mesenchymal stem cells in the dermis is also effective for improving the condition of and regenerating the dermis.
In addition, the present inventors have elucidated in greater detail the locations in which mesenchymal stem cells are present in the dermis and subcutaneous fat, and have found that platelet-derived growth factor-BB (PDGF-BB) is involved in the localization of mesenchymal stem cells, while also determining that promoting production of PDGF-BB in vascular endothelial cells contributes to increased production of and stabilization of mesenchymal stem cells (Japanese Patent Application No. 2010-209705).
Platelet-derived growth factor (PDGF) is a growth factor involved in regulation of migration and proliferation of mesenchymal stem cells including fibroblasts, smooth muscle cells and glia cells, and it is produced by a variety of cells such as epithelial cells and endothelial cells. At least 4 types of PDGF exist, PDGF-A, B, C and D, the A chain and B chain adopting homo or hetero dimer structures through formation of disulfide bonds, to produce the 3 isoforms (PDGF-AA, AB, BB). PDGF is known to exhibit its physiological action through PDGF receptor (PDGFR), a tyrosine kinase receptor. The gene for PDGF-B is known and has been genetically cloned (Non-patent document 30).
Discovering a component effective for promoting production of PDGF-BB is expected to be useful to promote production of mesenchymal stem cells and stabilize stem cells, and to thus be effective for a variety of purposes as described above.